Plasma cutting machine takes compressed air as its working gas, high temperature and high speed plasma arc as its heat source, melts the cut metal partially, blows away the melted metal with high speed current at the same time, and forms narrow cut gap. It can be used to cut metal materials such as stainless steel, aluminum, copper, cast iron, carbon steel and etc. This kind of cut has a high cut speed, narrow cut gap, neat cut, small heat affected area, small degree of workpiece deformation, simple operations, and remarkable energy-saving effect. It is applied to manufacture, installation and maintenance of kinds of machinery and metal structure, and cut, hole-making, digging, bevelling and etc. of middle thin planks.